1. Field of the Invention
The present invention relates to power impulse systems designed to generate power impulses of certain frequency and intensity for acting upon the medium being worked and has particular reference to percussive devices for creating impact impulses of high power.
This invention can be used to advantage in mining applications, for example, in machines for non-explosive mining in highly abrasive hard rock and in machines for breaking oversize rock pieces.
It can also be used in construction applications in machines for breaking old building foundations and walls, stripping road concrete coating, preparing rock beds for dams and other hydroengineering constructions, etc.
Further, this invention can be used in machine building, in rapid-action forging and swage hammers, in cutting machines, etc.
2. Description of the Prior Art
Known in the art is a percussive device (U.S. Pat. No. 3,601,988) for creating pressure impulses by means of working fluid. Said device comprises a receiver filled with a compressed gas and a power cylinder in which is fitted an impact piston which divides the interior space of said power cylinder into two chambers one of which is connected with the receiver and the other with the source of the working fluid. The device also comprises a means for returning the impact piston. Said means is constructed in the form of a hydraulic cylinder with a piston which divides the interior of the hydraulic cylinder into two spaces, front and rear. The hydraulic cylinder piston end at the front space mounts an impact piston arresting mechanism designed for catching the impact piston by its tail portion which passes from the first chamber of the power cylinder through the rear wall thereof into the front space of the hydraulic cylinder. Said tail portion of the impact piston has a bevelled surface on the end thereof. A groove with another bevelled surface is provided nearby. The impact piston arresting mechanism comprises a cup-shaped projection on the hydraulic cylinder piston. The wall of said projection has holes to accomodate cams designed for interaction with the tail portion of the impact piston during its initiating stroke and is provided with slots for passage of a crossmember. A barrel put on the cup-shaped projection has holes for sinking the cams at the release of the impact piston. The barrel is connected by means of said crossmember with a small piston movably mounted in a hole provided in the hydraulic cylinder piston. Provided on the back wall of the hydraulic cylinder is a stop designed for interaction with the small piston at the release of the impact piston.
At the initial stage of operation the impact piston is in the front position. When the pressure medium is fed into the rear space of the hydraulic cylinder, it moves the piston together with the arresting mechanism forward until the tail portion of the impact piston enters the cup-shaped projection, whereby the cams are caused to engage the groove in the impact piston tail portion. Thereafter the rear space of the hydraulic cylinder is put in communication with the outlet line, whereas the front space of said cylinder is connected with the source of pressure. The feed of the pressure medium into the front space of the hydraulic cylinder causes, first of all, movement of the small piston and the barrel, which is connected thereto by means of the crossmember, towards the back wall of the hydraulic cylinder, whereby the cams are locked in the engaged position. Then the hydraulic cylinder piston is caused to move, carrying therewith the impact piston by means of the cams interacting with the bevelled surface of the groove in the impact piston tail portion, forcing out the gas from the first chamber of the power cylinder into the receiver and compressing the gas still further. Thus the initiating stroke of the impact piston is completed. At the same time the working fluid is fed into the second chamber of the power cylinder. At the end of the initiating stroke of the impact piston the small piston is stopped by interaction with the stop on the back wall of the hydraulic cylinder, whereas the piston of the hydraulic cylinders continues moving. This results in shifting the barrel into the front position is relation to the cup-shaped projection, the barrel holes locating opposite the cams. By the action of the bevelled surface of the groove in the tail portion of the impact piston the cams are disengaged from said groove, thereby releasing the impact piston. The compressed gas in the first chamber of the power cylinder and in the receiver causes the impact piston to accelerate on its forward stroke, creating an impact pressure impulse in the working fluid. This completes the working stroke of the impact piston, whereupon the impact piston stops and the working cycle can be repeated.
In the percussive device under consideration, the means for returning the impact piston calls for expending energy of the pressure source on moving the hydraulic cylinder piston in both directions described herein, which causes need for employing substantially complicated arrangements for controlling the flow of the pressure medium. Furthermore, the disengagement of the cams from the impact piston tail portion is effected under load, which causes heavy wear on all the elements taking part in the disengagement process. The abovementioned disadvantages of the device under consideration substantially reduce its dependability.
Also known in the art is a percussive device (U.S.S.R. Inventor's certificate No. 202835) referred to as an impulse water jet. Said device has a barrel with a charging chamber for liquid under high pressure and is provided with a conical nozzle through which the liquid issues at a high velocity and which bounds the volume of the charging chamber at the front. A light piston is located in the charging chamber at the rear end thereof. Said piston separates the charging chamber from the interior space of a hydraulic cylinder with a heavy piston. Said heavy piston is adapted to reciprocate in the hydraulic cylinder and divides the interior space of the same into two spaces one of which is in constant communication with the atmosphere and the other is filled with oil.
The rear end of the light piston has a collet-type engagement arrangement designed for engagement of the light piston with the purpose of it being moved into the initial position by the heavy piston moving in the hydraulic cylinder. Provision is made of a receiver which adjoins said other space of the hydraulic cylinder and is separated therefrom by a partition having holes for passage of oil. The receiver serves the purpose of charging the water jet with a compressed gas and accomodates a piston with a drive mechanism rod passing therethrough. The end of said rod entering the other space of the hydraulic cylinder mounts an engagement arrangement which consists of a cup, an annular valve designed to discharge oil from the cup when engaging the heavy piston and admit oil into the cup when disengaging the heavy piston, an actuating spring, and a valve seat. To impart a reciprocating motion to the rod of the drive mechanism, use is made of the drive mechanism itself which may take the form of a crank gear or a hydraulic drive.
Preparatory to operation, the water jet is fed with water, the receiver is filled with a gas and the required oil pressure is built up in the other space of the hydraulic cylinder.
After the water jet is filled up with a gas and oil, and a liquid supply line is connected to the charging chamber, the heavy piston assumes the forward position, whereas the drive mechanism rod with the engagement arrangement takes the rearmost position. The drive mechanism moves said rod towards the heavy piston and the cup moves thereonto and encloses the oil in its interior (the inside cylindrical surface of the cup and the mating surface of the heavy piston are sealed), forcing it during further movement out of the cup interior into the other space of the hydraulic cylinder through a hole in the drive mechanism rod and the annular valve. When the cup interior is fully emptied of the oil, the activating spring expands and closes the valve onto the seat. During the return stroke of the drive mechanism rod the cup begins leaving the heavy piston, whereby the volume of the cup interior is increased and, as a result, the pressure inside the cup drops sharply and the oil pressure in the other space of the hydraulic cylinder becomes considerably lower. At the same time increase takes place in the forces which cause the heavy piston to follow the engagement arrangement and said heavy piston moves after the rod of the drive mechanism. The light piston, which is engaged to the heavy piston by means of the collet-type arrangement, moves therewith. On reaching a stop in the charging chamber, the light piston stops, the charging chamber is filled with liquid, and the heavy piston, on disengaging the collet, continues moving after the drive mechanism rod, forcing the oil out of the other space in the hydraulic cylinder through the holed partition into the receiver, whereby the receiver piston is moved and the gas in the receiver compressed.
When the drive mechanism rod approaches the rearmost position, the annular valve comes up against the holed partition and stops, the actuating spring becomes compressed and the annular valve becomes unseated, permitting the oil to rush from the other space in the hydraulic cylinder into the cup.
The energy stored in the compressed gas accelerates the piston in the receiver and the latter moves the oil, causing the heavy piston to move. The heavy piston accelerates, passes through the light piston collet and strikes the end of the light piston. The light piston transmits the energy to the liquid, the conical nozzle forms this liquid into a jet and the latter issues into the atmosphere at a high velocity.
After the jet is shot, all the mechanisms return into the initial position and the cycle is repeated.
The water jet under consideration has a substantially complicated construction with a large number of sealing elements and, like the previously described device, requires the use of a double-acting drive which is also substantially complicated.
All the disadvantages mentioned above adversely affect the dependability of the water jet.
Also known in the art is a percussive device referred to as a hydraulic hammer for breaking rock (U.S.S.R. Inventor's certificate No. 287657). Said device comprises a power cylinder which accomodates a piston with a rod. Said piston divides the interior space of the cylinder into two spaces, viz. a gas space and a liquid space. The device also comprises a hammer connected to said piston by means of said rod and adapted to reciprocate in guides provided with pneumatic dampers, a receiver designed for holding a compressed gas and connected with the gas space of the power cylinder, and a shutter located on the outside of the power cylinder and designed for opening large-section ports arranged to connect the liquid space of the power cylinder with the atmosphere. The front end of the hammer has a seat to receive a cylindrical tool for breaking rock. The receiver is made in the form of several pipes interconnected by the front and rear heads of the power cylinder and forming, in conjunction with said cylinder heads, the framework of the hydraulic hammer.
After the device is prepared for operation by charging the receiver with a gas to the required pressure, the piston, the hammer and the rod interconnecting these two parts are in the extreme forward position. When liquid is fed under pressure into the liquid space of the power cylinder, the piston and the hammer connected thereto by means of the rod move back, away from the rock, still further compressing the gas in the gas space of the power cylinder and in the receiver. After the movable system including the piston, the rod and the hammer reaches the rearmost position (when the hammer tool is at the maximum distance from the rock), the shutter moves on the power cylinder and opens the ports. Under the action of the compressed gas said system moves, accelerating, towards the rock, whereas the liquid is forced by the piston from the liquid space of the power cylinder through the ports into the atmosphere. The tool strikes the rock and the hammer stops. At this instant the shutter returns into the intial position, closes the power cylinder ports and the process is repeated.
In the device under consideration, the whole movable system, including the hammer, tool, piston, rod and a number of fastening, sealing and dampening elements, takes part in a blow, which adversely affects their working condition and, consequently, reduces the dependability of said device.